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Knee osteoarthritis: what the evidence says about exercise and physical therapy
Exercise is a first-line, strongly recommended treatment for knee osteoarthritis. What the guidelines and major trials show, including physical therapy vs. steroid injections.
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Osteoarthritis (OA) is the most common form of arthritis. The CDC estimates that about 33 million US adults have it [1]. Worldwide, 595 million people had osteoarthritis in 2020, and the knee was the most commonly affected joint [2].
If you have stiff, achy knees, especially on stairs or after sitting, here is what the research says actually helps.
Knee OA is expected to keep growing
The Global Burden of Disease study projects large increases in osteoarthritis cases between 2020 and 2050, mostly because people are living longer and the population is growing [2].
- Hand+48.6%
- Knee+74.9%
- Hip+78.6%
- Other joints+95.1%
Source: GBD 2021 Osteoarthritis Collaborators, The Lancet Rheumatology, 2023 [2].
The same study notes that osteoarthritis has no cure, which is exactly why treatments that reduce pain and keep people moving matter so much [2].
What the guidelines recommend
The 2019 guideline from the American College of Rheumatology and the Arthritis Foundation rates each treatment for knee OA. Here is a selection of the non-drug options [3]:
| Rating for knee OA | Treatments (selection) |
|---|---|
| Strongly recommended | Exercise; weight loss for people who are overweight; self-management programs; tai chi; a cane or a knee brace when pain or instability makes walking hard |
| Conditionally recommended | Balance exercises; yoga; cognitive behavioral therapy; heat or cold; kinesiotaping; acupuncture |
| Strongly recommended against | TENS; glucosamine and chondroitin; platelet-rich plasma (PRP) injections; stem cell injections |
Source: Kolasinski et al., 2019 ACR/Arthritis Foundation guideline [3]. The guideline also rates medicines and injections, which are not listed here.
A few points from the guideline are worth knowing:
- No single type of exercise wins. Walking, strengthening, neuromuscular training and water exercise are all options, “with no hierarchy of one over another,” and exercise “is associated with better outcomes when supervised” [3].
- Physical therapists help people get started and keep going. The guideline calls instruction from physical and occupational therapists “helpful, and often essential” for starting and maintaining exercise [3].
- Weight loss adds up. Losing 5% or more of body weight can make a difference, benefits keep growing with more weight loss, and results are better when weight loss is combined with exercise [3].
The international OARSI guideline agrees on the core: education and structured exercise programs, with or without weight management, are the foundation of care for knee OA [4].
Physical therapy vs. a steroid injection
In a trial published in the New England Journal of Medicine, 156 people with knee OA were randomly assigned to either physical therapy or a corticosteroid injection [5]. After one year, both groups had improved, but the physical therapy group had less pain and better function [5]:
| WOMAC score (0–240, lower is better) | Steroid injection | Physical therapy |
|---|---|---|
| At the start | 108.8 | 107.1 |
| After 1 year | 55.8 | 37.0 |
Source: Deyle et al., NEJM, 2020 [5]. The difference between groups was 18.8 points in favor of physical therapy.
Injections still have a place: the ACR guideline strongly recommends them for some patients [3]. The point is that physical therapy is not just a step to get through before “real” treatment. On its own, it produced lasting results.
What about knee replacement?
Surgery is the right choice for some people. In a Danish trial of 100 patients who were eligible for a knee replacement, surgery plus 12 weeks of non-surgical care gave more pain relief and function at one year than the non-surgical program alone, but also more serious adverse events (24 vs. 6) [6].
The non-surgical program (exercise, education, diet advice, insoles and pain medication) still led to meaningful improvement, and most people in that group (about 3 in 4) had not needed a knee replacement by the one-year mark [6]. For many people, a structured program is a reasonable first step, and it also prepares the knee if surgery comes later.
Why weight matters for your knees
In a study of older adults with knee OA, each pound of weight lost was linked to about a 4-pound reduction in the load on the knee with every step [7]. Over thousands of steps a day, that adds up.
The IDEA trial tested this further in 454 adults with knee OA over 18 months. People who combined diet and exercise lost an average of 11.4% of their body weight and had less pain and better function than those who did diet or exercise alone [8].
The takeaway
- Exercise is a strongly recommended, first-line treatment for knee osteoarthritis.
- Supervised exercise tends to work better, and a physical therapist can tailor it to your knee.
- In a randomized trial, physical therapy beat a steroid injection on pain and function at one year.
- If you carry extra weight, combining weight loss with exercise gives the best results.
You can start physical therapy in Utah without a referral. A first visit can tell you which exercises fit your knees and how to progress them safely.